Polyimide aerogel with controlled porosity: Solvent-induced synergistic pore development during solvent exchange process

Abstract

Despite intensive studies on polymer aerogels, the fabrication of polyimide aerogels mostly relies on supercritical drying; however, the development of suitable ambient or vacuum drying methods and a shortened solvent exchange process are important for industrial applications. This study highlights the effect of the solvent type used for the solvent exchange process on the porosity and pore structure of vacuum-dried polyimide aerogels. By combining two different solvents, we could achieve a much higher aerogel porosity than when using either solvent independently. This synergistic effect cannot be simply explained by the surface tension of the exchange solvent but is shown to be related to the solvent–polymer affinity, solvent-induced structural change during the solvent exchange process, and shrinkage behavior during the solvent exchange and drying processes. The pore structure and porosity are shown to be easily controllable by simply adjusting the solvent ratios. Moreover, the solvent exchange time is much shorter (~10 h) than that in previous reports on polyimide aerogels, which is highly beneficial for industrial application. The mechanical properties were highly dependent on the porosity and pore structure, and the relative permittivity could be adjusted in a wide range according to the controlled porosity. Together with high thermomechanical stability, various electronic applications are expected. Moreover, the idea proposed in this study is expected to serve as a useful guideline for the fabrication of various other polymer aerogels with efficient processability.